Stout is a dark, top-fermented beer with a number of variations, including dry stout, oatmeal stout, milk stout, and imperial stout.
The first known use of the word stout for beer, in a document dated 1677 found in the Egerton Manuscripts, referred to its strength. The name porter was first used in 1721 to describe a dark brown beer. Because of the huge popularity of porters, brewers made them in a variety of strengths. The stronger beers, typically 7% or 8% alcohol by volume (ABV), were called "stout porters", so the history and development of stout and porter are intertwined, and the term stout has become firmly associated with dark beer, rather than just strong beer.
Porter originated in London, England in the early 1720s. The style quickly became popular in the city, especially with porters (hence its name): it had a strong flavour, took longer to spoil than other beers, was significantly cheaper than other beers, and was not easily affected by heat. Within a few decades, porter breweries in London had grown "beyond any previously known scale". Large volumes were exported to Ireland and by 1776 it was being brewed by Arthur Guinness at his St. James's Gate Brewery. In the 19th century, the beer gained its customary black colour through the use of black patent malt, and became stronger in flavour.
Originally, the adjective stout meant "proud" or "brave", but later, after the 14th century, it took on the connotation of "strong". The first known use of the word stout for beer was in a document dated 1677 found in the Egerton Manuscript, the sense being that a stout beer was a strong beer. The expression stout porter was applied during the 18th century to strong versions of porter. Stout still meant only "strong" and it could be related to any kind of beer, as long as it was strong: in the UK it was possible to find "stout pale ale", for example. Later, stout was eventually to be associated only with porter, becoming a synonym of dark beer.
Because of the huge popularity of porters, brewers made them in a variety of strengths.